Spark discharge metal depositing apparatus



July 16, 1963 KlYOSHl INOUE 3,098,150

SPARK DISCHARGE METAL DEPOSITING APPARATUS Filed June 13, 1960 3 Sheets-Sheet 1 lI/II/II/l/ IN VEN TOR. x/yasw/ M/OUE BY WM 621% m A rI'OPA/ V y 1963 KIYOSHI INOUE 3,

SPARK DISCHARGE METAL DEPOSITING APPARATUS Filed June 13, 1960 5 Sheets-Sheet 2 /0 ac. 501/205 r/Z 4 D.c'. 5'0UEC'6' y. INVENTOR.

7 K/VOSH/ woof BY M4w (M44 A r raw/75 United States Patent 3,tl8,150 SPARK DISCHARGE METAL DEPQSITING APPTUS lltiyoshi Inoue, 182 Yoga Tamagawa Setagaya-ku, Tokyo, Japan Filed .Iune 13, 1960, Ser. No. 35,693 13 Claims. (Cl. 219-69) This invention relates to new and improved apparatus for treating metal surfaces and more especially for depositing on a metal surface a coating of similar metal or a different metal or metal alloy. The invention is herein illustratively described by reference to the presently preferred embodiments thereof; however, it will be recognized that certain modifications and changes therein with respect to details may be made without departing from the underlying essentials involved.

A variety of purposes may be served by use of the process and apparatus disclosed herein. For example, a portion or all of a work piece surface may be coated with a layer of metal for decorative effects, in which case any of different ornamentally attractive metals may be used. Instead, the purpose may be to achieve a high corrosion resistance, in which case the metal deposited on the work piece will be chosen for that purpose. Alternatively, the coating may be for the purpose of reducing the coefficient of friction of the surface. In still other cases, hardening of the work piece surface may be intended, in which event such metals as tungsten alloys or other extremely hard materials may be deposited, as in the case of treating the cutting edges of saws, tool bits, etc.

A broad object of this invention is to provide a method and apparatus which is commercially practicable, is rapid in operation, efficient, and readily implemented in terms of available components and materials. A related object is to provide such a method and apparatus wherein substantial areas may be coated to a relatively uniform thickness within a reasonably short period of time.

A more specific object is a new and improved apparatus for the described purposes which may be manufactured either in the form of a hand tool which may be moved in a prescribed pattern back and forth over a work piece surface in order to apply a coating to a predetermined area of such surface or which may be implemented in the form of an automatic apparatus capable of performing the operation rapidly without manual attention. I

A further object is such an apparatus which is automatically self-regulating and which does not require mechanical-electrical switching devices in order to control the flow of current for spark discharge purposes nor for operating the mechanism by which the electrode is vibrated in relation to the work piece.

Still another object is such a device which in its preferred embodiments requires no mechanisms or parts which are subject to rapid wear or deterioration, so that maintenance and replacement of parts, with the exception of the necessary replacements of the consumable electrode, present no problem.

These and other objects together with the novel features and advantages of the invention will become evident as the description proceeds in connection with the accompanying drawings.

FIGURE 1 is a series of diagrams depicting sequential phases in an operating cycle of the apparatus wherein metal is deposited by the combined intermittent spark discharge, electric contact and mechanical vibration effected between an electrode and opposing work piece.

FIGURE 2 is a simplified schematic diagram of an electric circuit for the apparatus.

FIGURE 3 is a somewhat simplified and partially schematic diagram of one form of the apparatus for Efi-QS ,150 Patented July 16, 1963 2 depositing metal, a portion of the apparatus being shown in longitudinal section.

FIGURE 4 is a circuit diagram for a modified embodiment of the invention.

FIGURE 5 is a side elevation view of the modified apparatus which may be connected in the circuit of FIGURE 4.

FIGURE 6 is a simplified diagram of a second embodiment representing an alternative to that shown in FIG- URE 5, likewise utilizing the circuit of FIGURE 4.

FIGURE 7 is a simplified side View of still another embodiment, wherein the electrode comprises means for feeding powdered metal into the spark gap for increasing the efficiency of the depositing process.

FIGURE 8 is a simplified diagram of still another embodiment featuring means for creating an atmosphere of inert or other gas in the spark discharge region, in connection with the depositing operation.

FIGURE 9 is a schematic diagram of a circuit of the type shown in FIGURE 2, including an improvement therein.

FIGURE 10 is a schematic diagram of still another improvement, wherein the necessary power for vibrating the electrode in relation to the work piece is derived primarily from a source separate from that producing the spark discharge action.

Referring initially to FIGURE 1, in diagram (at) the machining electrode 10, which is usually connected with the positive pole of a direct voltage source, is shown poised above the work piece 12, with the latter connected to the negative pole or terminal of the source (not shown). As the oppositely charged electrode and work piece approach each other, a spark discharge occurs between them when the gap becomes sufiiciently narrow, as illustrated in diagram (b). The attendant heat and mechanical forces developed in the spark discharge cause partial melting and partial evaporation of the opposing discharge surfaces, leaving crater formations 10a and 12a as depicted in diagram (c), wherein the spark discharge has terminated,or substantially so, yet the electrode continues to move toward the work piece. By immediately bringing the electrode and work piece together in a hammering action as in diagram (d), to establish direct electrical contact therebetween, short-circuit current will commence to flow between the electrode and work piece producing I R heating of the points of contact due to the contact resistance. This heating action melts the contacting ridges and tends to weld the parts together due to the high temperatures attained, at which point the contact resistance drops and the parts commence to cool, as suggested in diagram (e). Mechanical pressure between the electrode and Work piece is necessary in order to create this condition, which thereby destroys or deforms the craters Ma and 12a. This pressure is achieved by the hammer-like impact between the electrode and work piece. However, before the fused metal cools significantly the electrode is abruptly with drawn from the work piece and the weld is broken (diagram (1) Because the electrode is relatively thin or is less capable of conducting heat away from the region of contact than is the work piece, the body of metal nearest the work piece cools and thereby recovers its strength more quickly than that nearest the electrode, so that when the contact is suddenly broken by the application of a reverse force separating the electrode and work piece, more metal is left in bonded contact with the work piece than with the electrode and the result is a depositing of some of the electrode metal on the work piece, diagram (g). Diagram (h) illustrates the fully retracted position of the electrode representing a starting position as depicted in diagram (a) preparatory to the initiation of a succeeding cycle.

In accordance with an important principle and feature of this invention, the electrode and work piece are vibrated rapidly in air into and out of contact with each other at a high frequency, such as of the order of between 100 and 500 cycles per second, and each cycle of vibration involves the sequence depicted in FIGURE 51. While the electrode is being vibrated in relation to the work piece in this manner, producing the required rapidly intermittent spark discharge heating, electrical-mechanical contact, contact resistance heating, and mechanical interruption or severance, the electrode is moved gradually across the face of the work piece in any selected pattern in order to produce the required coating or deposit of metal on the work piece. Typically, the voltage used is of the order of 200 volts D.-C. and the machining current is of the order of 20 amperes, more or less. Deposition thicknesses of between 0.05 millimeter and 0.5 millimeter are readily achieved, and while usually the polarity of the electrode and work piece is as depicted in FIGURE 1, in some instances it is permissible or desirable to use the opposite polarity.

Whether the machining electrode or the work piece 12 will be covered or coated depends upon the choice of metals used and upon the polarities used. When using tin as the machining electrode and lead as the work piece, to name one exceptional case, negative electrode polarity is desirable. This is also true of a limited number of additional exceptional cases, whereas in general the usual situation requires positive polarity for the electrode. When the thickness of the deposit reaches a certain value, the electrical resistance of the work piece surface will increase to such an extent that the depositing speed will be reduced, so that it is no longer practicable to attempt increasing the thickness of the coating still further, due primarily to the fact that the depositing process, when carried on in the atmosphere, produces some oxidation of the deposited metal, which causes a large increase of electrical resistance. As later explained herein, the process may be performed in an inert gas, in which case greater depositing thicknesses may be achieved without appreciable loss of efiiciency due to oxidation.

Referring to FIGURES 2 and 3, an energy storage condenser 14 is connected across the electrode 10 and work piece 12 and is arranged to be charged from a direct current source 16 through an inductance element 18. As shown in FIGURE 3, this inductance comprises the coil of an electromagnet having a U-shaped or other suitable ferromagnetic core 20 which is mounted on supports 22 within a tool casing 24. The casing is provided with a handle 25 so that it may be held and moved in relation to the surface of work piece 12. Within the casing is mounted a separately insulated spring arm 26 which projects outwardly through an aperture 24a in one side of the casing and carries an electrode socket 28 having an electrode-receiving bore which is oriented transversely to the surface of work piece 12. A thumb screw 30 in the holder 2 8 permits holding the electrode in position and provides for the convenient repositioning and replacement of electrodes therein. The work piece 12 is held on a suitable supporting base '32 by means of clamp elements 3 1, such base and thereby the work piece being normally connected to the negative side of the power source 16. Typically, condenser 14 may have a capacity of between 200 microfarads and 1200 microfarads, whereas coil 18 may have a magnetizing force (in conjunction with the source 16) of the 1000 ampere turns.

An electromagnet armature 36 mounted on the cantilever spring arm 26 in position to be attracted upwardly against the pole faces of the electromagnet core 20 causes the electrode to be raised from the work piece surface in response to energization of electromagnet coil 18. Resilience of the spring arm 26 normally urges the electrode 10 into firm electrical and physical contact with the work piece 12. When this contact exists, direct current flows from the source 16 through the coil 18 and produces 1 R heating of the contact interface between the electrode and work piece as indicated in diagrams (d) and (e) in FIGURE 1. However, the resultant magnetomotive force developed by energization of coil 18, which becomes maximum after the contacting points of metal have been heated sufiiciently to fuse them together and thereby reduce the contact resistance, produces a force of attraction between the core 20 and the armature 36 which abruptly lifts the arm 26 and thereby abruptly and forcibly breaks the contact between the electrode 10 and work piece 12, as indicated in diagrams (f) and (g) in FIG- URE 1. With the contact thus broken, condenser 14 is no longer short-circuited and is free to charge. Charging of the condenser from the D.-C. source 16 is expedited by the fact that the inductive reactance of coil 18, which tends to maintain the state of current flow in itself, produces an additional self-induction voltage which is additive to the voltage of source 16 in charging the condenser. By the same token, the condenser furnishes an extremely low-impedance circuit for dissipation of the magnetizing current flowing in the coil 18, so as to expedite deenergization of the coil and thus reduction of the force of attraction between the core 20 and the armature 36. Consequently, as the condenser is charged, the coil 18 is deenergized and the spring reaction force of the spring arm 26 again becomes eflective to force the electrode 10 back toward contact with the work piece 12. As the electrode approaches the work piece, the diminishing gap or spacing between them permits a spark to jump between them, as shown in diagram (b), FIGURE 1, thus initiating a succeeding cycle of operation.

The resulting action of the apparatus is a continuous rapid vibration of the electrode 10 in relation to the work piece 12 wherein the electrode and work piece themselves serve as contacts of electric switching means controlling the energization and deenergizartion of the vibratory coil 18 and the associated condenser 14. No other switching mechanism is required and no problem of wearing of electric switch contacts or of mechanical wear of moving parts is involved. The electrode 10 is intended to erode as a means to deposit metal on the work piece 12 and is thereby progressively advanced in its holder 23, either by means of periodic manual readjustments or by means of suitable feed mechanism (not shown) by which it may be continuously fed as necessary in order to maintain the desired average spacing between the electrode and work piece surfaces. The mechanism is evidently extremely simple and yet is extremely efiicient and rapid in its operation. The frequency of vibration of the electrode may be established by proper choice of the effective moment of inertia of the moving portion of the system, the stiffness of the spring arm 26, the value of the inductance 18, the magnetic characteristics of the electromagnet in other respects, the size of the condenser 14 and the voltage and impedance of the DC. source circuit. These involve well known design considerations and are matters of choice through which vibrational frequencies of any practical or desired value may be readily attained.

It will further be noted that the most forceful action which occurs during the vibrational cycle, namely, the magnetic force of attraction of the armature 36, occurs on the lift phase of the cycle, that is the phase which retracts the electrode from the work piece. This is necessary in order to produce the required abrupt and substantial force necessary to separate the temporarily interwelded or fused surfaces of the electrode and work piece. The less positive and less abrupt action comprising the return force of the spring arm 26 is utilized for returning the electrode to the work piece in the remaining phase of the operating cycle. Consequently, there is little tendency for the electrode to adhere to the work piece and it is readily possible to obtain a uniform coating on the surface.

In one type of application, the method and apparatus is usable to harden the surface of the work piece. Electrode materials usable for surface hardening include any of the ultra-hard alloys, such as carbides, nitride alloys, hard pure metals, etc. Materials used for the electrode will depend upon the work piece metals, of course, to some extent and also the application for the process. Another application is that of decreasing the coefficient of friction of the work piece surface, in which case chromium may be used as the depositing metal, or an alloy of iron and chromium. In order to harden the edges of cutting tools, such as tool bits, drills, milling cutters, etc., ultra-hard alloys and graphite are suitable as electrode material. Ferro-chrome alloy is suitable for hardening the blades of gas turbines which are operated in clean gas or air. Aluminum is considered best for hardening or surfacing the blades of gas turbines to be used under conditions wherein the atmosphere contains carbon or ashy substance. By use of this invention, for example, a cutting bit has been sufficiently hardened to prolong its useful life by from two and one-half to four times, Whereas the useful life of a band saw blade has been prolonged in actual practice by from three to four times that of a conventional blade. In addition, the process may be used to mark or stamp products. Ornamental markings or informational markings may be applied to metal surfaces using any of different depositing metals, such as silver or copper. In certain cases the machining electrode may be impregnated with a minute quantity of a radioactive substance such as P-32 in order to apply an identifying or distinguishing mark on the work piece surface which may be detected by any radioactive sensitive detecting device. Furthermore, coatings, protective and otherwise, may be applied, such as in the case of applying copper as a coating to steel wire, applying stainless steel to cast iron, applying gold or silver to brass or copper, etc. There is almost a limitless number of applications and combinations of metals that may be used with this invention.

In FIGURES 4 and 5 and subsequent figures, parts which bear similar reference numerals to those in FIG- URES 2 and 3 are similar in nature, whereas parts which bear similar reference numerals primed generally correspond to those in the preceding figures. Thus, in this instance, the electrode and work piece 12 are connected across the storage condenser 14 which is charged through the series-connected inductance 1-8 from the D.-C. source 16. Coil 13 is mounted in the upper por- ,tion of a tool housing 24 having the handle 25'. In the lower portion of this housing is mounted a second inductance or coil 40 in coaxial alignment with the coil 13. Electrically the coil 40 is connected directly across the terminals of D.-C. source 16. The twocoils within the housing 24 surround a nonmagnetic guide sleeve or tube 42 which extends lengthwise of the housing and serves as a guide for the ferromagnetic armature piece 44 which is connected to the rod 46 serving as a support for the electrode holder or socket 28. The rod 46 extends through the ferromagnetic armature 44- to its upper end which is connected to a coil spring 48 secured to the upper end of the housing 24'.

In essence, the second coil 40 performs part of the function of the spring arm 26 in the preceding embodiment in that it provides a continuous but yieldable force which urges the armature 44 and thereby the electrode holder 28 toward the work piece 12. This force is considerably smaller, however, than the force of retraction exerted on the armature 44 when the coil 18' is fully energized during the operating cycle. When the electrode 10 is brought into contact with the work piece 12, the coil 18 draws the armature 44 upwardly and breaks the contact, thereby permitting condenser 14- to recharge and also permitting the force of coil -40 to urge the armature downwardly again. Spring 48 tends to maintain the armature 4-4 in a substantially neutral position wherein it partially overlaps each of the coils 18' and 40. Moreover, the spring 48 is helpful in stabilizing the vibration 6 which results from the alternate energization and deenergization of coil 18.

FIGURE 6 illustrates a modification which is particularly useful in case of work pieces having high electrical resistance. In this instance, the circuit path through the work piece is made very short by providing two electrodes mounted on a common mechanical support 6% carried on the end of the spring arm 26'. The two electrodes are connected to respectively opposite sides of the energy storage condenser 14 and are positioned close to each other but at a suflicient spacing so as to preclude arcing directly between them. In this case, the spring arm 26 carries a ferromagnetic armature 36a cooperable with the electromagnet 18" and a ferromagnetic armature 36b cooperable with the electromagnet 40. The coils of these clectromagnets correspond to the similarly numbered coils in FIGURE 4, the coil of magnet 18" being serially connected with D.-C. source 16 and storage condenser 14- and the coil of electromagnet 40' being shunted across the source 16. Another advantage of the arrangement in FIGURE 6 is that the work piece 12 and its support 32 need not be connected to the source 16. Only during the brief instants of electric contact between both electrodes and the work piece 12 is there any connection of the work piece to the source. The electrodes 10a and 1011 are preferably of the same material, although if desired they may be of different materials. The electrode assembly is moved gradually over the work piece in order to complete the desired coating in the area to be covered. In the modification shown in FIGURE 7, the electrode holder 28 and vibrating apparatus, including spring arm 26, may be generally similar to that shown in FIGURE 3, for example. In this case, however, the electrode itself, 100, is not consumed during the process of depositing metal on the work piece 12, but serves as a means to pour powdered metal M through its central bore 100' onto the work piece 12 and to apply electric potential to the powdered metal during the deposition thereof. In this example, [the upper end of the electrode is provided with a threaded nipple 70 to which is connected the reservoir or container 72 of powdered metal, by means of the threaded collar 74. As the electrode is vibrated up and down in relation to the work piece 12, the powdered metal is agitated and is fed down through the hollow interior of the electrode 100 in order to pour out onto the surface of the Work piece 12. The operating cycle of the apparatus is otherwise generally similar to that described in the preceding emhodiments, wherein as the electrode approaches the work piece a spark is formed which heats and melts the powdered metal in this instance and also the underlying area of the work piece. In this instance, however, there is no substantial tendency for the electrode itself to become welded to the work piece 12 and therefore the process of separating the electrode from the Work piece in the last half of the vibration cycle does not involve a fracturing or disrupting of a Welded contact. Instead the powdered metal which had been melted and fused to the surface of the work piece remains in contact therewith whereas that which is still within [the bore of the electrode ltlc is not fused solid or otherwise ibonded to any other part. Such a device is lfiOllIld to :be capable of depositing large quantities of metal in a relatively short period of time and with comparatively small quantities of energy consumed.

In FIGURE 8 the electrode 1nd also has a central bore extending throughout its length, but in this instance comprises a consumable electrode. Its upper end is supported in the holder 8%) which includes a valve chamber 82 having a needle valve 84 therein adapted to cooperate with the valve port 86. The valve port 36 is connected through a hose 88 to a source 90 of pressurized inert gas. The electrode holder is mounted on the rockable lever arm 92 pivoted intermediate its ends at M and normally urged in a direction to press the electrode against the work piece 12 by means of the return spring 96. The

electromagnet 98 cooperating with the ferromagnetic armature mounted on the lever arm 92 provides a magnetic force of attraction which tends to separate the electrode from the work piece when the electromagnet is energized. The electromagnet is connected in circuit with the D.-C. source 16 and condenser 14 in the same manner as the magnet coil in FIGURE 2.

During operation of the apparatus shown in FIGURE 8 inert gas flows at a rate established by the positioning of the valve $4 and blankets the region in which the spark discharge and electric current flow occurs between the electrode and work piece. This minimizes any tendency for oxidation to occur in the deposited metal. Thus, if the inert gas is argon, for example, the metal depositing operation is still effected at low cost, because the modifications and additions necessary to provide the gaseous medium are relatively inexpensive. Moreover, it is possible to deposit metal with greater thickness efliciently because or" the reduction of oxidation. It is possible in this instance to practically double the thickness of the deposited metal without decreasing the eificiency any more than when depositing to maximum thickness under atmospheric conditions. If the gaseous medium delivered to the electrode 10d is of a high heat absorption type such as Trigen, greater preheating of the metal takes place during the spark discharge action and somewhat increased efliciency is achieved. If desired, the electrode apparatus may be housed in an air-tight chamber and the gas which is delivered through the hollow electrode may be recovered and reused. This is an obvious revision and its illustration is therefore omitted from the figure.

In the modification shown in FIGURE 9 the direct current source 16' comprises the alternating current generator 16'a and the three-phase rectifier bridge 1672. If desired, suitable filtering or smoothing network elements may also be incorporated in the voltage supply 16', although they generally are unnecessary. The remainder of the circuit is basically similar to that shown in FIG- URE 2, the electrode 10 being connected to one side of the energy storage condenser 14 and the Work piece 12 being connected to the other side thereof. The storage condenser is connected to be charged from the source 16' through the coil of the electromagnet coil 18 (see FIG- URE 3). The electromagnet cooperates with the ferromagnetic armature 36 and the associated return spring 26 in order to form a vibratory system. Connected in shunt with the electromagnet coil 18 is a variable inductance 116. The function of this variable inductance is to provide for adjustment of the elfective ampere turns of the coil 18 as may be necessary or desirable when the magnitude of the electric current flowing between the electrode and work piece is changed as by a change of machining conditions, such as the materials used, the voltage of the source, etc. Usually there is an optimum degree of excitation of the electromagnet coil 18 in order to provide maximum efficiency and speed of operation of the apparatus and this may be established or set by observations and measurements, or through trial and error by varying the setting of the inductance 110. In the further modification shown in FIGURE 10, the storage condenser 14 is connected directly across the D.-C. source 16 as are the electrode 1%)- and work piece 12. In this instance, however, the electromagnet coil 18 is not serially connected between the source 16 and the storage condenser 14 but is connected in a separate circuit including an additional direct curent source 120 across which the electrode and work piece 10 and 12 are also connected. Thus, the energizing voltage for coil 18 is derived from the source 129, whereas the spark discharge voltage for the metal depositing function proper is derived primarily from the source 16. As a matter of fact, however, because the condenser 14 is connected not only across source 16 but also across source 120 and because the electrode and work piece are likewise connected across both sources, a certain small portion of the total charge on the condenser 14 is derived from the source 120 and a certain small portion of the direct current flow between the electrode and work piece which occurs during the mechanical contact phase between these elements is derived from the source 126. The intermittent contact and separation between the electrode and work piece still serves as the means by which vibration is established in the system, as well as intermittent charging and dischargring of the condenser 14. That is, the basic self-switching and self-vibrating action of the system is provided in the circuit of FIGURE 10 as well as in the circuit of FIG- URE 2, even though in this case a separate source of driving power for the electromagnet is provided as a supplement to the system.

These and other aspects of the invention will be evident to those skilled in the art based on the foregoing description of the preferred embodiments thereof.

I claim as my invention:

1. Apparatus for depositing metal on a work piece, comprising a voltage source, a first conductor for connecting such a work piece to one side of said source, an electrode, a second conductor for connecting said electrode to the opposite side of said source, thereby to form a discharge circuit including the electrode and work piece, an apparatus base including electrode support means adapted for positioning the electrode in contact with the work piece non-fluid environment, means for initially biasing said electrode into contact with said work piece, said electrode support means being movable on said base to permit relative vibrational movement of the electrode into and from contact with such work piece and including means normally applying force between the support means and work piece for driving the electrode against the work piece with hammer-like abruptness thereby to draw a spark discharge creating a partial weld therebetween, electromagnet means mounted on said base and operable when energized to draw the electrode support means abruptly away from the work piece to break the weld, the electrode being thermally less conductive than the work piece and drawing heat from the weld at a slower rate, whereby metal from the electrode is left deposited on the work piece when the Weld is broken, said electromagnet means including a coil connected in said circuit to be energized momentarily by flow of cur rent serially through the electrode and work piece during the brief instant of contact therebetween, thereby to effect vibration of the electrode by the attendant switching action of the electrode making and breaking contact with the work piece, and an energy storage capacitance connected in shunt across the electrode and work piece to be charged thereby during that portion of the vibration cycle in which the electrode is withdrawn from the work piece and to discharge through the spark gap therebetween during relative approach movement of the electrode and work piece, said capacitance preventing arcing between the electrode and work piece as the same are being separated.

2. Apparatus for depositing metal on a work piece, comprising a voltage source, a first conductor for con necting such a Work piece to one side of said source, an electrode having less conductance thermally than the work piece, a second conductor for connecting said electrode to the opposite side of said source, thereby to form a discharge circuit including the electrode and work piece, an apparatus base including electrode support means adapted for positioning the electrode in contact with the work piece in a non-fluid environment, means for initially biasing said electrode into contact with said work piece, said electrode support means being movable on said base to permit relative vibrational movement of the electrode into and from contact with such work piece and including means normally applying force to the sup port means tor driving the electrode against the work piece with hammer-like abruptness, thereby to draw a spark discharge creating a partial weld therebetween, electromagnet means mounted on said base and operable when energized to draw the electrode support means abruptly away from the work piece to break the weld and leave electrode metal deposited on the work piece, said electromagnet means including a coil connected in said circuit to be energized momentarily by flow of current serially through the electrode and work piece during the brief instant of contact therebetween, thereby to effect vibration of the electrode by the attendant switching action of the electrode making and breaking contact with the work piece, and an energy storage capacitance connected in shunt directly across the electrode and work piece to be charged thereby through said coil during that portion of the vibration cycle in which the electrode is withdrawn from the work piece and to discharge through the spark gap therebetween during relative approach movement of the electrode and work piece.

3. The combination defined in claim 2, wherein the capacitance is connected directly in shunt across the electrode and work piece, with the coil interposed serially in one of the conductors leading from the source, and a second voltage source connected directly in shunt across said capacitance.

4. In apparatus for coating a work piece with metal, the combination comprising two separate sources of voltage Lhaving terminals thereof interconnected, an electromagnet coil interposed in one of the connections, a storage capacitance shunted across one source between said source and said coil, a discharge electrode and a work piece positioned in a non-fluid medium, means for initially biasing said electrode into contact with said workpiece, said discharge electrode and work piece connected respectively to opposite sides of said capacitance, said electrode having less thermal conductance than the work piece, said electromagnet means including relatively movable elements magnetized by energization of said coil and arranged to efiect relative separation between said electrode and work piece, and means yieldably urging said work piece and electrode relatively together with hammer-like abruptness, whereby said coil and the attendant switching action effected by alternate making and breaking of contact between the electrode and work piece produce vibration therebetween and progressive electrode deposit of metal on the work piece, said capacitance means suppressing arcing across the gap between electrode and work piece as the same are being separated.

'5. In apparatus for coating a work piece with metal, the combination comprising a source of voltage, a storage capacitance shunted across said source, an electromagnet coil interposed in the connection between one side of said capacitance and said source, discharge electrode means and a work piece positioned in a non-fluid environment, means for initially biasing said electrode into contact with said work piece, said discharge electrode and said work piece connected serially across said capacitance, said electrode having less thermal conductance than the work piece, said electromagnet means including relatively movable elements magnetized by energization of said coil and arranged to effect relative separation between said electrode means and work piece, and means yieldably urging said work piece and electrode means relatively together with hammer-like abruptness, whereby said coil and the attendant switching action effected by alternate making and breaking of contact between the electrode means and work piece produce vibration therebetween and progressive deposit of metal on the work piece, said apparatus including means suppressing arcing across the gap between electrode and work piece as the same are being separated.

6. The combination defined in claim 5, wherein the last-mentioned means comprises a spring member acting on the electrode to urge the same into contact with the work piece.

7. The combination defined in claim 5, wherein the last-mentioned means comprises an electromagnet having a coil connected across the voltage source and acting on the electrode to urge the same into contact with the work piece.

8. The combination defined in claim 5, and a variable inductance connected in circuit with said coil to permit varying the effective ampere turns thereof.

9. The combination defined in claim 5, and means ejecting an inert gas into the spark gap and contact region of the electrode and work piece.

10. The combination defined in claim 5, wherein the electrode has a passage therethrough opening into the spark gap region, and means to feed powdered metal through such passage into the spark gap region of the electrode and work piece.

11. The combination defined in claim 5, wherein the electrode means comprise two separate electrodes supported side-by-side and conjointly vibrated into and from contact with the work piece, said electrodes being connected respectively to opposite terminals of said source.

12. The method of coating :1 work piece with a metal deposit comprising rapidly vibrating an electrode into and from hammering contact with the work piece in a gaseous medium, discharging a brief impulse of current through the contacting surfaces of the electrode and work piece each time they come into contact with one another, terminating current flow between them as soon as contact is broken to avoid arcing, and moving the vibrating electrode across the Work piece over a prescribed area to coat such area.

13. The method defined in claim 12, wherein the electrode comprises a radioactive material and the resultant coating is thereby rendered radioactive.

References Cited in the file of this patent UNITED STATES PATENTS 2,273,819 Cooke et a1. Feb. 24, 1942 2,796,509 Blake June 18, 1957 2,967,226 De Bruijn I an. 3, 1961 

1. APPARATUS FOR DEPOSITING METAL ON A WORK PIECE, COMPRISING A VOLTAGE SOURCE, A FIRST CONDUCTOR FOR CONNECTING SUCH A WORK PIECE TO ONE SIDE OF SAID SOURCE, AN ELECTRODE, A SECOND CONDUCTOR FOR CONNECTING SAID ELECTORDE TO THE OPPOSITE SIDE OF SAID SOURCE, THEREBY TO FORM A DISCHARGE CIRCUIT INCLUDING THE ELECTRODE AND WORK PIECE, AN APPRATUS BASE INCLUDING ELECTRODE SUPPORT MEANS ADAPTED FOR POSITIONING THE ELECTRODE IN CONTACT WITH THE WORK PIECE NON-FLUID ENVIRONMENT, MEANS FOR INITIALLY BIASING SAID ELECTRODE INTO CONTACT WITH SAID WORK PIECE, SAID ELECTRODE SUPPORT MEANS BEING MOVABLE ON SAID BASE TO PERMIT RELATIVE VIBRATIONAL MOVEMENT ON ELECTRODE INTO SAID FROM CONTACT WITH SUCH WORK PIECE AND INCLUDING MEANS NORMALLY APPLYING FORCE BETWEEN THE SUPPORT MEANS AND WORK PIECE FOR DRIVING THE ELECTRODE AGAINS THE WORK PIECE WITH HAMMER-LIKE ABRUPTNESS THEREBY TO DRAW A SPARK DISCHARGE CREATING A PARTIAL WELD THEREBETWEEN, ELECTROMAGNET MEANS MOUNTED ON SAID BASE AND OPERABLE WHEN ENERGIZED TO DRAW THE ELECTRODE SUPPORT MEANS ABRUPTLY AWAY FROM THE WORK PIECE TO BREAK THE WELD, THE ELECTRODE BEING THERMALLY LESS CONDUCIVE THAN THE WORK PIECE AND DRAWING HEAT FROM THE WELD AT A SLOWER RATE WHEREBY METAL FROM THE ELECTRODE IS LEFT DEPOSITED ON THE WORK PIECE WHEN THE WELD IS BROKEN, SAID ELECTROMAGNET MEANS INCLUDING A COIL CONNECTED IN SAID CIRCUIT TO BE ENERGIZED MOMENTARIALY BY FLOW OF CIRRENT SERIALLY THROUGH THE ELECTRODE AND WORK PIECE DURING THE BRIEF INSTANT OF CONTACT THEREBETWEEN, THEREBY TO EFFECT VIBRATION OF THE ELECTRODE BY THE ATTENDANT SWITCHING ACTION OF THE ELECTRODE MAKING AND BREAKING CONTACT WITH THE WORK PIECE, AND AN ENERGY STORAGE CAPACITANCE CONNECTED IN SHUNT ACROSS THE ELECTRODE AND WORK PIECE TO BE CHARGED THEREBY DURING THAT PORTION OF THE VIBRATION CYCLE IN WHICH THE ELECTRODE IS WITHDRAWN FROM THE WORK PIECE AND TO DISCHARGE THROUGH THE SPARK GAP THEREBETWEEN DURING RELATIVE APPROACH MOVEMENT OF THE ELECTRODE AND WORK PIECE, SAID CAPACITANCE PREVENTING ARCING BETWEEN THE ELECTRODE AND WORK PIECE AS THE SAME ARE BEING SEPARATED. 